1. Field of the Invention
The present invention concerns a method of and an apparatus for decomposing wastes in a chemical plant of decomposing wastes containing by-products formed in a chemical plant by using super-critical or high pressure/high temperature water and capable of recovering and reutilizing raw material compounds or derivatives thereof as an aimed product in a plant from the wastes. More in particular, it relates to a method of and an apparatus for decomposing wastes such as PET bottles and urethane foams by using super-critical water and high pressure/high temperature water and recovering the raw material compounds or the derivatives thereof from the wastes.
2. Description of the Prior Art
In the case of industrially synthesizing various chemical products in chemical plants, it is well-known that by-products other than aimed products are formed or unreaction products remain. For example, in a polymerizing reaction plant, a device for separating a resultant polymer and unreacted monomers in a reaction vessel is essentially provided and the recovered unreacted monomers are generally reutilized as the raw material for the polymerizing reaction. It is also known that oligomers are by-produced in the polymerizing reaction and separation/elimination steps of the oligomers are often conducted since aimed properties can not be obtained or the properties are worsened with lapse of time if the oligomers are left in the polymers. While the unreacted monomers can be reutilized by merely incorporating them again into a raw material feed line, the oligomers are subjected to incineration or discarding since they can not be handled in the same manner as the monomers.
Side reaction products or oligomer such as dimers or trimers of aimed compounds are formed not only in polymerizing reaction plants but also in chemical plants for synthesizing low molecular compounds, and such by-products or oligomers have to be separated from the aimed compounds by, for example, distillation. While by-products can be separated from low molecular materials relatively easily, since separation of the aimed compound from the oligomers is often difficult, a great amount of the oligomers and the aimed compounds are often contained after all in the wastes such as distillation residues. There are scarcely no methods of effectively utilizing such wastes and they are merely subjected to incineration or discarding treatment, which brings about a problem with a view point of resource saving.
In recent years, it has been attempted to detoxicating wastes or obtain utilizable products therefrom by using hydrolyzing or oxidizing reactions in super-critical water or high pressure/high temperature water. For example, Japanese Patent Laid-Open Hei 3-500264 discloses a method of detoxicating wastes in a discharge liquid system by utilizing oxidizing reaction under a super (or sub)-critical state, Japanese Patent Laid-Open Hei 5-31000 discloses a method of hydrolyzing various high molecular compounds by using water at a super-critical or subcritical state and, further, Japanese Patent Publication Hei 3-16328 or Japanese Patent Laid-Open Hei 5-271328 discloses a method of obtaining pure terephthalic acid and glycol from polyethylene terephthalate wastes.
However, although the technique of Japanese Patent Laid-Open Hei 3-500264 is important as a detoxicating method, it involves a problem for the usefulness of the resultant materials since the method accompanies oxidizing reaction and other publications mention nothing about methods and apparatus of efficiently decomposing wastes in chemical plants containing oligomers such as dimers.
In view of the above, in the present invention, wastes in a chemical plant which can not be utilized but are merely incinerated or discarded have been noted and it is an object of the invention to establish a continuous treating method capable of decomposing target compounds such as by-products or oligomers contained in the wastes and decomposing them into raw material compounds or derivatives thereof for aimed compounds in the plant.
The present invention provides a method of decomposing wastes containing target compounds having one or more of hydrolyzable bonds of ether bond, ester bond, amide bond and isocyanate bond wherein the method comprises continuously supplying wastes in a molten state or a liquid state to a reactor, continuously supplying super-critical water or high pressure/high temperature water to the reactor and bringing the water into contact with the wastes thereby decomposing the target compounds, and recovering them as raw material compounds or derivatives thereof for the target compound.
The present invention further provides an apparatus for decomposing wastes comprising:
a reactor,
means for continuously supplying wastes containing target compounds having one or more hydrolyzable bonds of ether bond, ester bond, amide bond and isocyanate bond as they are in a molten state or liquid state to the reactor continuously,
means for supplying super-critical water or high pressure/high temperature water to the reactor, and
means for introducing a discharged liquid containing decomposition products of the target compounds discharged from the reactor into a separation device.
The decomposing method of the present invention can be applied with no particular restriction to wastes in a chemical plant so long as they contain hydrolyzable target compounds and, among all, the method is applicable effectively when the target compound is xe2x80x9cdimer or higher oligomer of raw material compoundxe2x80x9d as the by-product in a case where the aimed compound in the chemical plant is a high molecular material, or xe2x80x9cdimer or higher oligomer of the aimed compoundxe2x80x9d as by-products in a case where the aimed compound is a low molecular material. By using the decomposing method of the present invention, both xe2x80x9cdimer or higher oligomer of raw material compoundxe2x80x9d and xe2x80x9cdimer or higher oligomer of aimed compoundxe2x80x9d can be decomposed into xe2x80x9craw material compound or derivatives thereofxe2x80x9d, so that resultant decomposition products can be utilized effectively. xe2x80x9cOligomerxe2x80x9d in the present invention means dimer or higher compound with no restriction for the numerical value of the polymerization degree since it varies depending on the kind of the polymer or the polymerizing method.
In the method of the present invention, it is preferred that the super-critical water or high pressure/high temperature water to be supplied to the reactor is set to higher than 100xc2x0 C. and higher than 5 MPa, and to supply the supercritical water or high pressure/high temperature water in an equal or more amount based on the weight of the wastes in the chemical plant.
The feature of the decomposing method according to the present invention resides in that the target material is wastes in a chemical plant in a molten state or liquid state and that useful compounds can be recovered continuously from the wastes. Since the wastes in the chemical plant are discharged continuously, s storage vessel for the wastes is necessary in the batchwise treating method. Further, the batchwise process involves a problem that loss of energy is large for cooling or temperature elevation of the reactor upon batch replacement. Further, since a great amount of water is necessary for slurrifying solid-state wastes upon charging them, an energy for putting them to a high temperature is required. In the method according to the present invention, however, since the wastes in the chemical plant can be treated continuously as they are in a molten state or liquid state under constant pressure and temperature conditions, it is free from the foregoing drawbacks and extremely useful in actual operation.
The target to be decomposed in the present invention is wastes in chemical plants containing target compounds having one or more of hydrolyzable bonds of ether bond, ester bond, amide bond and isocyanate bond. When the target compound in the wastes is xe2x80x9cdimer or higher oligomer in the raw material compoundxe2x80x9d as by-products in a case where the aimed compound is a high molecular material or xe2x80x9cdimer or higher oligomer of the aimed compoundxe2x80x9d as by-products in a case where the aimed compound is a low molecular material, wastes can be reutilized particularly effectively by the application of the method of the present invention, so that a great advantages can be provided. In the present specification, xe2x80x9cdimer or higher oligomerxe2x80x9d is merely referred to as an oligomer.
Among preferred target compounds, those classified as oligomers of raw material compounds can include, for example, polyester oligomers (having ester bond) such as polyethylene terephthalate, polyamide oligomers (having amide bonds) such as nylon and polycarbonate oligomers (having ether bonds). The polyester oligomers include cyclic ester oligomer or chained oligomer which can be decomposed into a dicarboxylic acid such as terephthalic acid and a diol. The nylon oligomers include cyclic or chained oligomers synthesized from xcex5-caprolactom as a raw material and xcex5-amino capronic acid as ring-opened derivative of xcex5-caprolactom can be obtained therefrom. Further, the polycarbonate oligomers can be decomposed into a polyhydric alcohol or polyhydric phenol and carbonic acid as the raw material.
Further, compounds formed by self-polymerization of cyclic ether bond-containing compounds such as epichlorhydrine, ethylene or propylene oxides are oligomers containing ether bonds which may be present both as xe2x80x9coligomer of raw material compoundxe2x80x9d or as xe2x80x9coligomer of aimed compoundxe2x80x9d. That is, if they are oligomers by-produced upon synthesis of a polymer by using the compounds, they are oligomer of the raw material compound. On the other hand, if they are oligomers by-produced upon synthesis of the compounds, they are oligomers of the aimed compound.
Furthermore, since self-polymerizates having ether bonds are by-produced also upon synthesis of pentaerythritol or like other compound, such oligomers are xe2x80x9coligomer of the aimed compoundxe2x80x9d, which are preferred target compounds in the present invention.
xe2x80x9cOligomer of the aimed compoundxe2x80x9d can also include those oligomers of compounds such as oligomers of di- or tri-isocyanate compounds (having amide bonds) that cause self reaction and can form hydrolyzable bonds. The isocyanate compound can include, for example, tolylene diisocyanate (2,4- or 2,6-TDI) or diphenyl methane diisocyanate (MDI) and such oligomers are target compounds for decomposition. The compounds obtained after the decomposition are diamine compounds as the intermediate material upon synthesis of isocyanates and they are, for example, tolylene diamine or diphenyl diamino methane.
The present invention is also applicable to by-products which are not oligomers, namely, by-products formed from side reactions of raw materials. In this case, raw material compounds or derivatives thereof can be obtained after decomposition. If an aimed compound and oligomers are less separatable, both of them sometimes may be present mixed together in separably in wastes from the chemical plant. Since the present invention is based on the premise of effectively utilizing the wastes, it is also the feature of the present invention to decompose an aimed compound which can not but be incinerated because of inseparability from other materials into the raw material compound for reutilization. In view of the above, it is also within the scope of the present invention that the aimed compound itself is contained in the target compound. Further, in the present invention, aimed compounds which are obtained in the chemical plant but are discarded as products out of the standards can also be the target compound. Further, when the aimed compound is a high molecular compound, molding products thereof can also be the target compound.